#!/usr/bin/env python
"""
Solution to Project Euler Problem 8
http://projecteuler.net/

by Apalala <apalala@gmail.com>
(cc) Attribution-ShareAlike
http://creativecommons.org/licenses/by-sa/3.0/

Find the greatest product of five consecutive digits in the 1000-digit number.
"""
import functools
import itertools
import operator


TARGET = """
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450
"""

TARGET = ''.join(TARGET.strip().split())


def largest_product_of(n, k):
    n = [int(c) for c in str(n)]
    return max(
        functools.reduce(operator.mul, itertools.islice(n, i, i + k), 1)
        for i in range(len(n) - k)
    )


def test():
    assert 9 == largest_product_of(TARGET, 1)
    assert 81 == largest_product_of(TARGET, 2)
    assert 5832 == largest_product_of(TARGET, 4)


def run():
    print(largest_product_of(TARGET, 13))


if __name__ == '__main__':
    test()
    run()
